STM32 I/O pins are 5V-tolerant. I2C devices use open-drain outputs. I currently see no problem with operating an I2C bus with 5V devices from a 1.8V STM32 (with pullups to 5V). Is my understanding correct?
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Yes. I just recently had an opportunity to test this. You must set the GPIO to Open Drain mode with no pullup but then it works fine. All of the pins that can be I2C pins are qualified to be 5V tolerant according to the ST Micro documentation.
Chuck
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Would it work in Interrupt mode too? Or should it be only in Open Drain mode? – Matthieu Dec 10 '18 at 13:46
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Have look at this answer : 1.8v is probably too low to have good timings since its far from expected 5v.
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1Not quite the same. That answer involved 3.3V pullups being misinterpreted by a 5V device. This involves interpretation of 5V pullups by a 1.8V device with tolerant I/O pins. – Adam Lawrence Feb 01 '13 at 14:35